Virus-like particles have been found to assemble in yeast expressing brome mosaic virus coat protein due to viral replicative processes. Cryo - TEM and image reconstruction has shown the presence of 28 nm T=3 particles which strongly resemble native virus, as well as a novel 25 nm form. We have now formed particles in yeast by expressing the coat protein and various packagable RNAs from expression constructs. We propose to analyze these particle populations by Cryo-HRSEM to determine the relationships of true virus, the T=3 particles, the 25 nm particles, and the new particle to their varying properties.